Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $67.41   11.762%   $75.3388   $75.34   $75.35   $75.30  
  Purchase #2 $230.54   4.549%   $241.0273   $241.03   $241.05   $241.00  
  Purchase #3 $199.32   12.231%   $223.6988   $223.70   $223.70   $223.70  
  Purchase #4 $127.45   12.198%   $142.9964   $143.00   $143.00   $143.00  
  Purchase #5 $173.34   3.325%   $179.1036   $179.10   $179.10   $179.10  
  Purchase #6 $211.92   10.670%   $234.5319   $234.53   $234.55   $234.50  
  Purchase #7 $223.88   12.590%   $252.0665   $252.07   $252.05   $252.10  
  7 purchase totals = $1,233.86       $1,348.7633   $1,348.77   $1,348.80   $1,348.70